Alarm system



ALARM SYSTEM Filed June 19, 1923 Patented Apr. 16, 1929.

UNITED STATES 1,709,097 PATENT OFFICE.

WILLIAM C. ROE, OF NEW YORK,

N. Y., ASSIGNOR TO HOLMES ELECTRIC PROTECTIVE COMPANY, OF NEW YORK, N. Y., A, CORPORATION OF NEW YORK.

ALARM SYSTEM.

This invention relates to alarm systems and particularly to burglar alarm systems.

It is an object of the invention to provide a new and improved burglar alarm system which requires a minimum of operating current and in which the danger of defeating the system is reduced to a minimum.

The operation of practically all protection circuits depends upon a change in the current values in the circuit, brought about by a variation of the resistance of the circuit. By

employing a normally energized relay in such a system, it is an easy matter to sound an alarm when a break occurs in the protection wiring, or when the current has dropped below a predetermined value, but experience has shown that it requires very close adjustment and supervision to record a short-circuit in the wiring. This is due to the fact that the current in the circuit must at all times be very carefully adjusted, since a slight increase or decrease will tend to operate the alarm relay which is normally held from operation by v a counter-force, such as a spring, justsufficient to offset the magnetic attraction on its armature. Furthermore, a short-circuit across the extreme end of the protective wiring does not cause the same change in current value as when the short-circuit occurs at the beginning of the wiring, and unless the resistance is very carefully adjusted, it is sometimes possible to short-circuit the wiring at certain places without sounding the alarm. It

is therefore quite obvious that such a system,

' requires frequent attention and adjustment and that it is readily affected by natural causes such as slight changes in the applied voltage and the resistance of the circuit.

In accordance with certain features of the present invention, means are provided whereby an alarm circuit may be operated practically Without supervision and independently of changes in current and resistance. To accomplish this result, in the preferred form of the invention, means is provided for shortcircuiting the entire protective wiring upon a short-circuit occurring across any part thereof. Thus, if a burglar should short-circuit the very end of the protective wiring, the alarm will be given in fully as quick and positive a manner as when the short-circuit occurs at the center or, in fact, any other part of the wiring.

Other features and advantages of the invention will appear from a consideration of the following description taken in connection with the accompanying drawing, which illustrates diagrammatically a protection circuit embodying the features of the invention.

Referring to the drawing, the protection circuit includes a galvanometer 4, and a battery 5 preferably located in a central office, and a relay 6 and a suitable protective network 7 located on the subscribers premises. The relay 6 has two windings 8 and 9 which are connected, respectively, to the ends of the network 7. The windings 8 and 9 are equal in the effective ampere turns and resistance and are differentially connected, as shown in the drawing, thus making the relay 6 absolutely neutral when the current traverses the whole loop circuit. The normal protection circuit may be traced from'the positive side of battery 5, through galvanometer 4, conductor 10, one side of the network 7 conductor 11, winding 9 of differential relay 6, a conductor 12, the other side of network 7, conductor 13, winding 8 of differential relay 6, to the negative side of battery 5. In this system, the relay 6 is not afi'ected by any change in voltage, resistance or current, and therefore it'can be adjusted to practically any degree of sensitivity without difiiculty. One important feature of this system is that the windings 8 and 9 of the differential relay constitute only a very minute part of the resistance of the circuit, and the current passing through either winding would normally be enough to operate the relay if that winding was not opposed by the other winding. Thus, the relay will be sure to operate when the winding 9 is cut out by a short-circuit at any part of the loop. Upon the operation of the relay 6, in accordance with a feature of the invention, an armature 14 is attracted to close a. looking a circuit for relay 6, which serves to short-circuit the entire protective network 7. The locking circuit for the relay 6 may be traced from the positive side of battery 5, through galvanometer 4, conductor 10, conductor 15, armature 14 and associated relay contact, winding 8 of the relay 6, to the negative side of battery 5. It will be seen that since the relay 6 is operated by a shortcircuit at any part of the network 7, the alarm signals 19 and 20 will be operated at the central station in every case. Furthermore, the locking circuit serves to hold an alarm signal indefinitely, as the relay 6 will remain in its operated condition until the circuit is momentaril broken between the rela. and the source 0 current 5.

Ihe galvanometer 4 is provided with a pointer 16 and a pair of oppositely disposed alarm contacts 17 and 18, respectively. In the preferred embodiment of the system, the pointer 16 will be moved to the right to engage the alarm contact 18 when the resistance of the circuit is changed due to the establishment of the short-circuit through the armature 14 of the relay 6. When a break occurs in the protective network 7 the pointer 16 will be moved to the left to engage the contact 17. The engagement of the pointer 16 with either of the contacts 17 or 18 will serve to operate the visual signal 19 and the audible signal 20.

It will be evident, from the above description, that a short-circuit in any part of the protective wiring will have the same efiect upon the differential relay, and also that any current or resistance changes in the circuit will not afiect its functioning provided, of course, the current value is maintained above the minimum required for its operation.

The invention claimed is: v

In an alarm system, a central station including a source of current and indicating means responsive to current flow above and below a predetermined normal in circuit therewith a circuit extending from said source and indicating means including a protective network having lines extending throughout an area to be protected and having adjacent sides and ends, a differential relay having two windings, one of said windings being connected between a source and a protective area and means connecting the other winding of said'relay between the ends of the network farthest from the source, whereby said second winding will be shortcircuited by a cross between the conductors at any portion of the network, and means operated by the relay armature for shortcircuiting the network between said wind- WILLIAM G. ROE. 

